What Exactly Is the Dense Packing Design Principle for UHPC Base Materials?

The tight packing design principle of UHPC base materials achieves maximum density arrangement of solid particles by optimizing particle gradation, incorporating ultra-fine powders, and controlling particle size distribution, thereby reducing porosity and improving material density and performance. Based on 28 years of material R&D experience, Qinglong Group believes that a high-quality UHPC tight packing system should achieve porosity ≤5% and a most probable pore size ≤100nm. This design is realized through scientific mix proportion optimization and process control, laying the foundation for the high strength and high durability of UHPC.

Particle gradation optimization is the core of tight packing. A continuous gradation system is adopted, with coarse aggregate maximum particle size ≤1mm, fine aggregate fineness modulus of 2.3-2.6, and ultra-fine powders (such as silica fume and slag powder) with particle sizes of 0.1-10μm. In the Nanning Wuxiang China Resources MixC project, Qinglong Group optimized aggregate gradation using the Fuller curve, achieving a packing density of 2.4-2.6g/cm³ and reducing porosity to below 4%. This gradation design ensures that large and small particles fully fill each other, reduces voids, and improves matrix density.

Ultra-fine powders fill micropores. The particle size of admixtures such as silica fume is 1/100-1/50 that of cement, effectively filling the gaps between cement particles. In Qinglong Group's UHPC formula, silica fume content is 10%-20% and slag powder content is 20%-30%, significantly improving the microstructure. Water-binder ratio control is also critical: a low water-binder ratio (0.18-0.22) reduces capillary pores and increases strength. Through these measures, the UHPC matrix achieves optimal packing.

Process control ensures the realization of the design. Mechanical mixing ensures uniformity, and vacuum dewatering removes large air bubbles. Qinglong Group has introduced German equipment to achieve precise control. Tight packing design is the cornerstone of UHPC's high performance and deserves great attention.